The present invention relates to a process for the indigo dyeing of yarns in skeins or hanks.
As is known, the indigo dyeing of yarns is generally performed by means of so-called open width dyeing plants and so-called rope yarn plants.
In practice, open width plants use reels of yarn on which a large number of yarns, generally 350 to 400, is arranged; the yarns are arranged side by side and are passed in succession through the dyeing baths and rewound at the opposite end on reels in which the yarns are again arranged side by side.
In rope dyeing plants, dyeing is performed on a series of so-called ropes; each rope is constituted by a large number of yarns, generally 350 to 400, which are arranged side by side so as to define in practice a rope; said series is dyed by passing it in succession in a certain number of dyeing vats and, after the drying step, is placed in containers (one container per rope); the containers are then subjected to the separation of the yarns in order to arrange said yarns on reels (one container per reel) in which the yarns are arranged side by side.
This type of dyeing, which produces reels with a large number of yarns arranged side by side, is certainly useful if the weaving of fabrics is performed; in such weaving it can be useful to have the various yarns arranged side by side and wound on the same reel.
However, this arrangement does not allow to use the yarns in knitting machines, since it is necessary to have the yarn available on a spool.
Attempts made so far to dye the yarn arranged in skeins have not yielded satisfactory results, since the bath which is used for dyeing in skeins undergoes rapid degradation and change of characteristics, so that the dyeing does not have uniformity characteristics on the yarn.
Other known solutions, which provide for execution during the reeling of the yarn in ropes, by means of the separation of the yarns into groups of yarns which can then be subjected to a subsequent spooling step, are considerably complicated, since they require a long series of operations.